JSON to Kotlin Converter

About this tool

Paste a JSON sample and get Kotlin type definitions you can use immediately. Emits `@Serializable` data classes. Keys that are not valid Kotlin identifiers get a `@SerialName`.

When you would use it

• Kotlinx.serialization in an Android or Ktor project
• Bootstrapping models from a real JSON response instead of writing them by hand
• Keeping types in step with an API that has changed

Worked example

{
  "id": 4815,
  "name": "Ada Lovelace",
  "active": true,
  "score": 91.5,
  "roles": ["admin", "editor"],
  "address": { "city": "London", "postcode": "NW1" }
}

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
data class Root(
    val id: Long,
    val name: String,
    val active: Boolean,
    val score: Double,
    val roles: List<String>,
    val address: Address
)

@Serializable
data class Address(
    val city: String,
    val postcode: String
)

Things worth knowing

• Every object in an array is merged when inferring the shape, so a field missing from one item is marked optional rather than assumed to always be present.
• Identical nested shapes are de-duplicated into a single type instead of generating near-duplicates.
• Array element types are named from the singular of the field name, so posts produces a Post type.
• A sample with more records produces better types, because optional fields only reveal themselves across several examples.